1. Field of the Invention
The present invention relates to a surface nitriding member, and particularly relates to a surface nitriding member used preferably as a member such as semiconductor producing devices and liquid crystal producing devices which requires a corrosion resistance property.
2. Description of Related Art
As wiring in the semiconductors and liquid crystal panels become finer, fine workings with dry processing are progressing. With the demand for such fine workings, a halogen-based corrosive gas is used as a film forming gas or an etching gas for the semiconductors or the like.
On the other hand, it is known that aluminum nitride exhibits high corrosion resistance against such a halogen-based corrosion gas. Therefore, members having aluminum nitride on their surfaces have been used in the semiconductor producing devices, the liquid crystal panel producing devices and so on.
When aluminum contacts air, its surface is oxidized to form a thin oxidized film. Since the oxidized film is an extremely stable passive phase, the aluminum surface can not be nitrized by a simple nitriding method. Under the circumstances, the following methods have been developed to modify the surface of aluminum and form aluminum nitride thereon.
Japanese Patent Laid-Open Publication No. 60-211061 (JP-A-60-211,061) discloses a method in which, after the inner pressure of the chamber is reduced to a given pressure, hydrogen gas is introduced therein to perform a discharging. Such a discharging is effected to heat the surface of the member such as aluminum. Then, argon gas is introduced therein and discharging is effected to activate the surface of the member, and the surface of the aluminum member is subjected to an ion nitriding by introducing nitrogen gas.
Japanese Patent Laid-Open Publication No. 7-166321 (JP-A-7-166,321) discloses a method in which a nitriding aid made of aluminum powder is contacted with the surface of the aluminum, and aluminum nitride is formed on the surface of the aluminum nitride by heating it in the nitrogen gas atmosphere.
However, according to the method described in JP-A-60-211,061, since aluminum nitride is formed by using the discharging, there is a drawback such that the entire device is complicated and thus a producing cost is increased. Further, there is also a drawback such that it is difficult to apply this method for nitride members having complicated shapes and large sizes.
Further, according to the method described in JP-A-7-166,321, since the nitriding aid is used, voids exist in a resulting surface layer of aluminum nitride so that denseness is not sufficient. For this reason, it is an actual situation that corrosion resistance against the halogen-based corrosive gas is not sufficient and it cannot be said to be practically satisfactory.
It is an object of the present invention to provide a surface nitriding member in which a nitriding member having a high corrosion resistance property with respect to a halogen-based corrosive gas is formed on its surface.
According to the invention, a surface nitriding member comprises a substrate made of metallic aluminum, aluminum alloy or aluminum-containing composite material, and a nitriding portion formed by nitriding a surface portion of the substrate, wherein the nitriding portion contains at least one element other than aluminum selected from Group 2A, Group 3A, Group 4A and Group 4B in Periodic Table and wherein a concentration of the element at a surface side of the nitriding portion is lower than that of the element at a substrate side of the nitriding portion.
These and other objects, features and advantages of the invention will be appreciated upon reading of the following description of the invention when taken in conjunction with the attached drawings, with understanding that some modifications, variations and changes of the same could be easily made by the skilled person in the art to which the invention pertains.